The present invention relates to an analog electronic timepiece for indicating the time by hands, more specifically, to a technology for reducing power consumption thereof.
A timepiece is not only for telling the correct time, but also has as an aspect of an accessory. In almost all of timepieces, external visual design occupies an important position.
Almost all of the recent timepieces such as wristwatches are electronic timepieces using quartz oscillators, which are of a digital type of indicating the time by numbers and an analog type of indicating the time by a dial and hands. In the analog electronic timepiece, the following two functions are required to be satisfied at the same time.
One of them is a function of rotating hands only fixed angles in a set period of time, and the other is a function of holding the hands to prevent occurrence of a hand-skip phenomenon against an external impact.
FIG. 19 is an expanded view showing the structure of train wheels in a driving part of a conventional analog two-hand electronic timepiece, and also shows concentric and coaxial gears expanded.
The rotation of a rotor 1a of a step motor is transmitted through a rotor pinion 2 to a fifth wheel gear 3, and through a fifth wheel pinion 4 rotating integrally with the fifth wheel gear 3 to a second wheel gear 5. Further, the rotation of the second wheel gear 5 is transmitted through a second wheel pinion 6 to a third wheel gear 7 and transmitted through a third wheel pinion 8 to a center wheel gear 9 to rotate a minute hand 15 which is mounted on the center wheel gear 9 via a center wheel shaft.
Furthermore, the rotation of the center wheel gear 9 is transmitted through a center wheel pinion 10 to a minute wheel gear 12 and transmitted through a minute wheel pinion 13 to an hour wheel 14, whereby the rotation is transmitted to an hour hand 17 mounted on the hour wheel 14. In other words, the rotational motion is bidirectionally transmitted through a train wheel mechanism from the rotor 1a to the hour hand 17.
In order to realize the aforesaid two functions in the analog timepiece at the same time, a step motor has been used conventionally. The step motor, as is generally known, can rotate by a fixed angle. Further, as having holding energy, the step motor can hold the hands at original positions against a disturbance energy to some extent which is generated by an external impact.
In designing the step motor, a required holding energy is set first in accordance with hands to be used, and then driving conditions of the step motor are set based on the holding energy. The power consumption when the step motor is rotated is almost determined by the driving conditions thus set.
Accordingly, the driving conditions are not optimized only from the viewpoint of driving, and thus if performance of hand motion is all that is required, there is a possibility that even smaller driving energy causes step motion. However, the set value of the holding energy is decreased to the above end, bringing about a problem that the hands can not be held when the disturbance energy exceeds the holding energy which has been set at a small value.
Therefore, a holding energy larger than the disturbance energy which occurs at the hands due to an external impact is set to thereby prevent a handskip phenomenon in the conventional analog electronic timepiece.
The magnitude of the disturbance energy relates to the magnitude of inertia in consideration of imbalance caused by degree of unbalanced moment of the hands. Concerning hands, since the shape of the hand is restricted, the disturbance energy is greatly influenced by the magnitude of inertia. For instance, if hands are made larger or different in shape from what should be, giving priority to visual design, whereby the disturbance energy easily exceeds the holding energy. Consequently, a hand-skip phenomenon occurs, resulting in impossibility of implementation of the aforesaid two functions of the analog timepiece.
For the above reasons, giving priority to visual design requires setting a holding energy at a large value, thereby necessarily increasing the power consumption of the step motor.
The present invention is made in view of the above-described background, and its objects are to eliminate limitations from an aspect of functions of a timepiece on visual design of a hand in an analog electronic timepiece to thereby allow a visually freely designed hand to be used regardless of the magnitude of a moment of the hand and to reduce power consumption.
To achieve the above objects, the present invention is structured as follows in an analog electronic timepiece (a two-hand electronic timepiece) composed of an hour hand and a minute hand for indicating the time, a step motor for rotating the hour hand and the minute hand, and train wheels for decelerating the rotation of the step motor and transmitting it to the hour hand and the minute hand.
The timepiece is configured such that a semicircular addition member having a radius equal to that of a root circle of a center wheel gear is firmly fixed to a half part on the center wheel gear sharing a center wheel shaft with the minute hand and a center wheel pinion on the opposite side to a direction in which a time indicating part of the minute hand extends with respect to the center wheel shaft to reduce a moment on the center wheel shaft caused by a combination of a center wheel composed of the center wheel gear, the center wheel pinion, and the center wheel shaft and the minute hand.
Further, to achieve the above objects, the present invention is structured as follows also in an analog electronic timepiece (a three-hand electronic timepiece) composed of an hour hand, a minute hand, and a second hand for indicating the time, a step motor for rotating the hour hand, the minute hand, and the second hand, and train wheels for decelerating the rotation of the step motor and transmitting it to the hour hand, the minute hand, and the second hand.
The timepiece is configured such that a semicircular addition member having a radius equal to that of a root circle of a second wheel gear is firmly fixed to a half part on the second wheel gear sharing a second wheel shaft with the second hand and a second wheel pinion on the opposite side to a direction in which a time indicating part of the second hand extends with respect to the second wheel shaft to reduce a moment on the second wheel shaft caused by a combination of a second wheel composed of the second wheel gear, the second wheel pinion, and the second wheel shaft and the second hand.
Further, instead of the fixation of the addition member to the aforesaid center wheel gear or the second wheel gear, it is also suitable that the center wheel gear or the second wheel gear is made such that a half part thereof including a tooth form on the opposite side is thicker than a half part on the side of a direction in which a time indicating part of the minute hand or the second hand extends.
Alternatively, it is also suitable that the center wheel gear or the second wheel gear is made such that a half part thereof on the opposite side is larger in density of its material than a half part on the side of a direction in which a time indicating part of the minute hand or the second hand extends.